A device is disclosed for continuous thermal treatment of granular bulk material, in particular for the crystallization of polymer granulate, such as polyethylene terephthalate (PET), with a product inlet terminating in a chamber being the very first chamber upstream and a product outlet after the last chamber downstream. In addition, a method is disclosed for the continuous thermal treatment of granular bulk material, in particular for the crystallization of polymer granulate, such as polyethylene terephthalate (PET), using the device.
A device is known from EP 0 712 703 A2, for example, which comprises a housing with an inlet and an outlet for plastic chips which are to be subjected to heat treatment. The interior of the housing is divided into a first large chamber and several smaller chambers by a plurality of separating walls, wherein the separating wall between the first chamber and the adjacent chambers is higher than the separating walls between the smaller chambers. All chambers can be supplied with gas from below via a sieve bottom to fluidize the chip product. During operation, the fluidized product flows via the upper edge of the respective separating wall from one chamber to the next. In the process, because of the effervescent movement in the respective fluidization chambers, undesired backmixing may occur as chips jump and/or are injected back from one chamber into the adjacent upstream chamber. This leads to different residence times for different chips, which necessarily causes differences in the product quality of the chips.
DE 195 00 383 A1 discloses a device for continuous crystallization of polyester material in granulate form. Thermal treatment is carried out in a cylinder-shaped treating space which is also supplied with gas from below via a sieve bottom in order to fluidize the granulate with the treatment gas. Although by using only a single treating space for fluidization purposes, cost savings are realized and stirring tools and the like are no longer necessary, this still does not make it possible to ensure a very narrow range of residence times of the particles and, consequently, a largely uniform product quality of the granulate.
EP 0 379 684 A2 discloses a device and a method for continuous crystallization of polyester material in granulate form. This device comprises two separately disposed fluidization chambers (fluidized bed apparatuses), wherein the first chamber is an effervescent fluidized layer with a mixing characteristic and the second chamber is a flow bed with a plug flow characteristic. While this combination of different fluidization chambers yields a surprisingly homogeneous product quality, each of the two separate fluidized bed apparatuses requires its separate circuit with channels, fans, heat exchanges for the gas injection and fluidization gas as well as cyclonic separators and/or filters for removing dust that is generated as a result of abrasion of the granulate particles.